Orange Syrup Cake with White Chocolate Buttercream

Cut
the orange into very thin slices, being careful not to cut them so thin
that they fall apart. Remove any seeds and toss the ends. Bring water
to a boil in a saucepan and blanch the orange slices for about one
minute. Drain and plunge slices into a bath of ice water. Drain again.

Meanwhile,
combine the sugar and 1 cup of water in a large saucepan. Cook over
medium heat until the sugar is dissolved without stirring, which may
cause crystals to form. If the pan is not heating evenly, simply swirl
the pan. Bring to a simmer and add the orange slices. Simmer - don’t
boil - for an hour and a half. Carefully remove slices from hot sugar
syrup and set on a cooling rack over a baking sheet until completely
dry, up to 24 hours. Reserve the syrup for brushing onto the cake
layers.

Preheat your oven to 350F. Oil and line three 9" round cake pans, then set aside.

Put
1/2 cup (99 g) sugar in a small bowl with the orange zest and rub
between your fingers until the sugar is very fragrant and looks like wet
sand. Whisk in the cake flour and baking powder then set aside.

In
a large bowl, whisk together the yolks, lemon juice, oil and vanilla.
Beat on medium-high until slightly lightened, about 5 minutes. Set
aside.

Pour the egg whites into a very clean large bowl. Begin
beating on medium-low until foamy, then turn the speed up to high and
gradually add the remaining 1 cup (198 g) of sugar. Beat until
moderately stiff peaks form (when lifting the beater from the bowl, the
peaks should droop slightly), being very careful not to whip the whites
until they are dry.

After the whites have been whipped, use a
rubber spatula to gently fold 1/4 of them into the yolk mixture. Add
another 1/4 of the whites and fold to combine. Repeat until all of the
whites have been incorporated, then sift in 1/3 of the dry ingredients.
Fold gently until few streaks remain, then add another third. Repeat,
continuing to fold very gently, until the last addition of dry
ingredients has been fully incorporated.

Divide batter evenly
between the prepared pans and bake for 15-20 minutes until the cake
springs back when pressed lightly in the center. Cool the cakes in
their pans on a wire rack for 10 minutes. Remove the cakes from their
pans and wrap them in plastic wrap then refrigerate them for at least 4
hours until they are completely cooled.

Cook
the egg whites and sugar in a small saucepan over medium heat, whisking
constantly, until the sugar is completely dissolved (test by rubbing
some between your fingers. If it's completely smooth, it's done). Pour
into another bowl (a stand mixer is preferable) and whip on high speed
until room temp. Then, on a medium-slow speed, add the butter, waiting
until each piece is completely incorporated before adding the next.
After all the butter has been added, turn the mixer back to high speed
and whip until it has come together, about five minutes. Add the
extract, beat briefly and then use.

If the buttercream seems
soupy after all of the butter is added and does not come together after
whipping, refrigerate for 5 to 7 minutes and continue whipping until it
becomes fluffy and workable.

Assembly

Cut the domes, if any, off the tops of the cakes.

Place
a layer of cake on your serving platter. Brush cake with orange syrup,
then top with a layer of buttercream. Add another layer of cake, brush
with orange syrup and spread evenly with frosting. Place remaining
cake on top and crumb coat with a small amount of buttercream. Frost
and decorate as desired, using candied orange as a garnish.